Fuel for and method of operating a jet engine



Wappingers Falls," N.Y., assignors to Texaco Inc., a corporationofDelaware No Drawing. Filed Dec.'27,-1955,S er.No.555,Z42

5 Claims; c1. so -35.4

invention relates to a novel composition having excellent hightemperature stability and a method for cooling heated materialsutilizing said composition.

The composition of the present invention has particular; application inthe operation of jet aircraft. The advanced high speed engines employedin jet aircraft have extremely high combustion temperatures and many ofthe materials which necessarily are exposed to such temperatures aredecomposed to the extent that they cannot perform their assigned tasks.Compositions used to lubricate the moving parts of jet engines, forinstance, may break down with a loss of viscosity and the formationofslud g'e and deposits which tend to prevent proper lubrication. It istherefore most important that some means or method be utilized to keepthese materials at temperatures in which they may function properly.

The use'ofthe jet fuel as a heat' sink for cooling vital aircraftcomponents such as the lubricating oil provides one solution to theproblem of high temperatures. This technique is exemplified by passingthe fuel in heat exchange relationship with thelubricating oil prior tofuel consumption. This use has imposed a new and serious fe'quirement ofextremely high thermal stability on jet fuel. Heat stability is of theutmost importance because/thermal degradation of the fuel will result incarbon build-up and clogging of the fuel lines and will in time preventoperation of the jet aircraft. Thermal stability has been imparted tojet fuel in two main ways, namely, by refining techniques such ashydrogenation and by the use of additives. This invention provides athermally stable jet fuel by the use of a particular type of additive.

In accordance with the present invention, an excellent-heat stablecomposition is formed by the addition of from 0.001 to 0.03 pencent byweight of at least one compound selected from the group consisting ofalkyl primary and alkyl secondary amines,- hav-ing atotal of from 16'to32 carbon atoms in thealkyl radicals, to a' major-portion of ahydrocarbon stock boiling within the range of from 250 to 700 F. Thepreferred addition range" of said alkyl amines is from 0.005 to 0.02percent by' Weight. The preferred alkyl primary amines in accordancewiththis invention are those having from'18 to 24 carbon atoms in atertiary alkyl radical. The preferred alkyl secondary amines are thosesubstituted with a tertiary C to C alkyl radical and Withanalkylsubstituted aralkyl radicalhaving-IO to 14 carbon atoms in thesubstituted alkyl group. Some examples of other primary amines which maybe used either individually or in mixtures with other amines inaccordance with this invention are as" follows: cetyl amine,Z-ethylpentadecyl amine, stearyl amine, neostearyl amine, behenyl amine,cerotyl amine, montaiiyl amine, myricyl amine, melissyl amine, laccerylamine, and ceromelissyl amine. Examples of'some useful secondary aminesare as follows: 2 isobutylhexyl-2-ethylhexyl benzyl amine, 2,2,5-

2,959,915 Patented Nov. 15, 1960 In order to demonstrate the superiorheat stability of'the composition'in accordance with the presentinvention, the base fuel alone and together with various types ofamine's have been tested in'an Erdco Fuel Coker Test Unit. When testingfuels with this unit, the f el under consideration is pumped through apreheater in the form of an annular heat exchanger? The heated fuel isthen passed through a heated sinteredsteel filter.

1 Sludge and sediment formed by the heating of the fueltrimethylhexylQ,2 diriiethyldecylbenzyl amine, 2-ethyl-2-butylnonyl-Z-hexyldecylbenzyl amine, neostearyl'myristyl deposit on thefilter. Test conditions on all the runs, the results of which arepublished in'the following tables, were as follows: preheatertemperature, 400 F.; filter temperature, 500 F.; fuel flow, 4 lbs./hr.;fuel pressure, 150'p.s.i.g. The thermal stability of a fuel is indicatedby the time for a filter'to partially plug. In order to determine this,the test is run until the drop in pressure (AP) across the filterreaches either 25 inches of mercury or a test duration of 5 hours. Agood fuel in this testis one which obtains a' filter AP below 20 inchesof mercury in five hours or more. r The base fuels with which theadditives were tested included a JP-4 fuel which is used by the militaryand commercial air lines and com-prises a mixture of about 65 percentgasoline and 35- percent light distillate. This product also adheres tothe following characteristics:

Gravity API n 45-57 Reid vapor pressure, lbs. 2:3 Freezing point max -76Smoke pt. volatility index min 54 Water reaction max; -1 Sulfur, percentmax 0.4 Mercaptan sulfur, percent (1) max 0005 Aromatics percent by vol.max 25 Olefins percent by vol. max 5.0 Bromine No. max 5.0 Potentialgum, mg./ 100 -max 14 Existent gum, mg./100 ml. max' 7 Heating value,B.t.u./lb. min 18,400 Distillation:

20% F. max 2 70 50% F. max 370 F. max 470' Another fuel used was aso-called JP4 Referee fuelwhichcan be described as a'specia'l grade ofJP4 fuel. The fuel is designed to be typical of lower quality JP'-4 fuelwhich would be available in wartime. It is used almost exclusively inthe developing and testing of mili-' tary jet engines; It'maybe furtherdistinguished from the ordinary JP-4 fuel by reference to the followingcharacteristics:

Gravity API 457-50 Smoke point volatility index 50-54 Sulfur, percent0.15-0.40. Heating value, B.t.u./lb. 18,40018,750 Distillation: r v n20% 250-290 50% 350-390 90% 450-490 The remaining characteristics areessentially the same asthose listed for the ordinary JP-4 fuel.

Still another fuel used for the investigation of' these ASTMdistillation:

IBP, F. 350

FBP 534 API gravity 37.9 Existent gum rng./100 ml 0.6 Accelerated gummg./ 100 ml 0.6 Sulfur, total wt. percent 0.027 Mercaptan sulfur, wt.percent 0.0009 Freezing point, F. 40 Heating value B.t.u./lb 18,473Aniline gravity constant 4991 Viscosity at 30 F. Q. cs 13.4 Volumepercent aromatics 21.8 Volume percent olefins 9.5 Smoke point, mm. Watertolerance Pass Flash point (P.M.), F. 150

The Erdco Fuel Coker Unit Test results with respect to heat stability ofjet fuels are set forth in the following tables. A mixture of C Ctertiary alkyl primary amines sold as Primene JM-R and a secondary amineof the general formula:

RNHR

wherein R is a mixture of C to C tertiary alkyl groups and R is a Calkyl substituted benzyl radical which was supplied as Ell-974, anexperimental amine, were the amines used in Table I.

1 Fuel shortage prevented completion.

The foregoing table demonstrates that alkyl primary and alkyl secondaryamines at concentrations of 0.018 weight percent (50 lbs./ 1000 bbl.)will greatly improve the heat stability of an unstable jet fuel.Although the run in which the additive Primene JM-R was tested was notcompleted due to fuel shortage, the negative AP indicates that the AP in300 minutes would still remain below zero.

The following table is set forth to compare the effectiveness of otheramines as heat stabilizing additives for jet fuels.

The product Armeen DM-18D is a tertiary amine which contains 92 percentof distilled dimethyl stearyl amine.

The foregoing table shows that a tertiary amine (Armeen DM-lSD) is of novalue as a heat stabilizing additive. Further, the table shows thataromatic amines,

represented by l-naphthylamine, diphenylamine and N,-N-di-sec-butyl-p-phenylene diamine at additive percentages of 0.018 byweight have no value as additives for heat stabilizing jet fuels.

These results further emphasize the unexpectedness of the fact that thealkyl primary and secondary amines of this invention are excellentadditives for high temperature fuel stability at surprisingly lowconcentrations.

0k. 50. 2 Fuel shortage prevented completion.

The above Table III demonstrates the effectiveness of a tertiary Gig-C24alkyl primary amine as a heat stabilizing additive at extremely lowconcentrations. Even at the extremely low concentration of 00018 percentby weight in a jet fuel (5 lbs./ 1000 bbls.) its effectiveness issurprisingly evident. Although a fuel shortage prevented the completionof this run, it is quite apparent that the fuel was effectivelystabilized by this small amount of additive.

In the development of an effective jet fuel additive it is alsonecessary to reject those additives which although effective inpromoting heat stability in the fuels, also lend to the fuel an affinityfor water. In order to determine a limiting value for the solubility ofwater in jet turbine fuels, the fuels must pass a water tolerance test.'The following is a description of the ASTMD109450T Water Tolerance Testof aircraft fuels which was used on the fuel compositions of thisinvention.

An ml. sample of the fuel to be tested is shaken vigorously at roomtemperature with 20 ml. of distilled Water in a ml. glass stoppergraduated cylinder for at least 2 minutes and thereafter allowed tosettle. The change in volume of the aqueous layer after 5 minutes ofsettling is reported to the nearest 0.5 ml. A pass rating denotes anincrease of 1 ml. or less in either layer. This change in volume istaken as the water tolerance of the fuel. The following table sets forththe results of water tolerance tests on various effective heatstabilizing additives.

Table IV Fuel Additive Water wt., percent Tolerance ZIP-4 Primene .TM-R0.009 Pass. JP-4 Primene JMR 0.0036 Do. JP-4 Primene JM-R 0.0018 Do. F-Primene JMR 0. 018 Do. F-105 alkyl-sec-amine 0. 018 D0. F 105polyoxyethylene sor laureate 0. 018 Fail. F-105 basic metal sulfonate 0.018 o F-105 Nitrogen substituted methacrylate polymer 0. 018 Do. F-105Nitrogen substituted methacryllate polymer 0.0061 Do. JP-4 Referee+normal barium sulfonate- 0. 018 Do.

It is evident from the above table that manyadditives although impartingeffective heat stability to fuels will fail to provide good watertolerance characteristics to the fuel composition and, therefore, beundesirable as jet turbine propellant additives.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and, therefore, only such limitations should beimposed as are indicated in the appended claims.

We claim:

1. A method of operating a jet aircraft comprising cooling the lubricantemployed in the lubrication of jet engines by indirect heat exchangewith a composition consisting essentially of a hydrocarbon stock boilingwithin the range of from 250 to 700 F. containing 0.001 to 0.03 percentby weight of at least one amine selected from the group consisting ofalkyl primary and alkyl, aralkyl secondary amines containing a total of16 to 32 carbon atoms in the alkyl radicals and subsequently using saidhydrocarbon for fuel for operation of said jet engine.

2. A heat stable jet fuel composition consisting essentially of a majorproportion of a hydrocarbon stock boiling Within the range of from 250to 700 F. and from 0.005 to 0.02 percent by weight of a compound havingthe general formula:

wherein R is selected from the group consisting of C to C alkyl groupsand mixtures thereof and R is a C alkyl substituted benzyl radical.

3. A method of cooling a jet aircraft component comprising passing thejet fuel composition, consisting essentially of a hydrocarbon stockboiling within the range of from 250 to 700 F. containing from 0.001 to0.03 percent by weight of at least one compound selected from the groupconsisting of alkyl primary amines having from 16 to 32 carbon atoms inthe alkyl group and a compound having a general formula:

amine.

5. A method of cooling the engine lubricant in a jet aircraft comprisingpassing the jet fuel composition consisting essentially of a hydrocarbonstock boiling within the range of from 250 to 700 F. containing from0.005 to 0.02 percent by weight of a tertiary'alkyl primary amine havingfrom 18 to 24 carbon atoms in the alkyl group, in indirect heat exchangerelationship with said lubricant.

References Cited in the file of this patent UNITED STATES PATENTS2,474,183 King June 21, 1949 2,573,471 Malina et a1. Oct. 30, 19512,607,665 Duncan Aug. 19, 1952 2,675,671 Malgieri Apr. 20, 1954 FOREIGNPATENTS 627,386 Great Britain Aug. 8, 1949

1. A METHOD OF OPERATING A JET AIRCRAFT COMPRISING COOLING THE LUBRICANTEMPLOYED IN THE LUBRICATION OF JET ENGINES BY INDIRECT HEAT EXCHANGEWITH A COMPOSITION CONSISTING ESSENTIALLY OF A HYDROCARBON STOCK BOILINGWITHIN THE RANGE OF FROM 250 TO 700*F. CONTAINING 0.001 TO 0.03 PERCENTBY WEIGHT OF AT LEAST ONE AMINE SELECTED FROM THE GROUP CONSISTING OFALKYL PRIMARY AND ALKYL, ARALKYL SECONDARY AMINES CONTAINING A TOTAL OF16 TO 32 CARBON ATOMS IN THE ALKYL RADICALS AND SUBSEQUENTLY USING SAIDHYDROCARBON FOR FUEL FOR OPERATION OF SAID JET ENGINE.